Air cleaning device and apparatus

ABSTRACT

An air cleaning device for removing aerosol particles from an air stream comprising: a particle charger comprising a housing and an electrode arrangement therein for generating air ions in the air stream, the particle charger having a particle charging zone within which, in use, aerosol particles in the air stream are electrically charged via collision with the air ions; a filter for precipitating electrically charged aerosol particles from the air stream moving through the device; and an air mover, comprising a casing, for moving the air stream through the device; wherein the particle charger and the air mover are provided upstream of the filter; and wherein the housing of the particle charger is hermetically sealed to the casing of the air mover in the direction of air flow through the device, such that the particle charger and the air mover are intimately coupled together, whereby all air entering the device has to pass through both the particle charger and the air mover.

The present invention relates to an air cleaning device and an aircleaning apparatus. The invention relates more particularly, but notnecessarily exclusively, to an electrostatic precipitation device and toan electrostatic air cleaning apparatus, both for use in air cleaningand filtration.

Air cleaning and other air filtration devices and apparatus are used toremove unwanted aerosol particles from air. Typically, air filtration isachieved using a filter component configured to entrap aerosol particlesfrom air as it passes through the filter.

Electrostatic precipitation air cleaning devices and apparatus operateby transferring an electric charge to aerosol particles in the air priorto their passage through the filter or particle collector componentthereof (hereinafter collectively referred to as a “filter” forsimplicity). An electric field may be applied to the filter, such thatsaid electrically charged particles are attracted to, and precipitatedonto, a surface of the filter during passage through thedevice/apparatus, thereby effecting removal of the particles from thepassing air stream with greater efficiency as compared to removal ofuncharged aerosol particles.

Electric charging of the particles can be achieved in a number of ways.One such way, utilising a “field charger”, is typically used infiltration applications. A field charger comprises a particle charger,which comprises an emission electrode and a counter-electrode, whichtogether are operable to form a particle charging zone. In use, anelectric field is established between the emission electrode and itscounter-electrode because of the difference in their respectiveelectrical potentials: the emission electrode is typically of a smallradius of curvature, e.g. it may be in the form of a fine conductingwire or sharp conducting pin, and is usually raised to a high voltage ascompared to the counter-electrode, which is typically held at earthedpotential. Such an arrangement leads to corona discharge at the emissionelectrode within the field charger (care being taken to ensure that thevoltage difference between the electrodes does not cause electricalbreakdown and lead to electrical arcing between the electrodes). Airions created by the corona discharge are accelerated by the electricalfield and collide with aerosol particles passing through the particlecharging zone, resulting in those particles becoming electricallycharged.

Prior art electrostatic air filtration devices and apparatus mostcommonly incorporate an array of thin wires (of the order of millimetresin diameter) as the emission electrodes in the field chargers therein.Such wire arrays form a corona discharge around every wire in the arrayand, therefore, can be shaped to fit numerous applications. However,wire arrays can be hindered by deposition of unwanted, deleterioussubstances on the wires, impacting charging effectiveness. Additionally,emission of ozone can be undesirably high from coronas supported onwires. Furthermore, because the wires have to be attached to supportingframework, in the regions of the ends of the wires where attachmentoccurs, corona emission is reduced to the extent that aerosol particlesin the air flowing past the ends of the wires are not effectivelycharged, which ultimately leads to reduced aerosol particle collectionefficiency. This “charge bypass” effect is usually exacerbated by therelative loose-fitting of the framework containing the wire array intosurrounding housing defining the flow path of air to be filtered passingthrough the device or apparatus.

Also known for use in field chargers, although much less commonly(indeed perhaps only by the present applicant), are “pin-type” emissionelectrodes. As compared to a wire array electrode, a pin-type electrodeforms a corona only in a relatively small volume around its sharp tip.The corona intensity at the tip of a pin-type electrode is higher ascompared to the corona intensity of a wire array electrode for a givenapplied current because of the physical differences between the two—theelectron concentration at a sharp (diminishing) point is greater thanthe electron concentration in a wire of substantially constantcross-section, which improves particle charging effectiveness.Furthermore, a pin-type emission electrode produces less ozone for agiven particle charging capacity as compared to a wire array equivalentbecause the corona distributed along a wire requires more electricalcurrent than a pin-type corona and ozone production is proportional tosaid electrical current. Moreover, as compared to wire array electrodes,pin-type electrodes are less affected by deposition of substances whichmight otherwise hinder corona discharge, the reason for this beingtwo-fold: firstly, the surface area of the sharp tip of a pin is muchless than that of the surface of a wire (around both of which coronadischarge occurs) and thus less deposition of corona-hinderingsubstances can occur, and secondly, the higher intensity of the coronaat the pin tip as compared to the corona along the length of the wireleads to a greater air ion flux at the pin tip which assists withprevention of deposition of, and flushing away of deposited,corona-hindering substances. Additionally, because a pin-type electrodedoes not have to be attached to surrounding framework in the same manneras is required for the wires of a wire array electrode, there are noregions of reduced corona emission with pin-type electrodes, which leadsto a higher proportion of aerosol particles being charged (as comparedto with a wire array electrode). Thus, despite the greater prevalence ofwire array emission electrodes in known field chargers, the use of apin-type emission electrode in a field charger offers many advantagesover and above those achievable with otherwise equivalent field chargerswhich incorporate wire array emission electrodes.

With either type of air cleaning device (i.e. using a wire arrayelectrode or a pin-type electrode in the field charger), an air mover,for example a fan, is typically incorporated to urge uncleaned air topass through the device. A usual arrangement of components in an aircleaner is, in the direction of airflow: particle charger, filter, airmover. Such a prior art arrangement is shown schematically in FIGS. 1 to3 of the accompanying drawings, which is typical of the air cleaningarrangement in a prior art portable air cleaning device.

Referring to FIGS. 1 to 3, there is shown therein a prior art, portableelectrostatic precipitation device 10 for removing unwanted aerosolparticles from an air stream. The electrostatic precipitation aircleaning device 10 comprises a particle charger 12, an air mover 15 inthe form of a mechanical fan, and a filter 16 for removing chargedaerosol particles from the air stream (“dirty air”) (not shown) as itflows through the device 10 via an inlet 17 at the entrance to theparticle charger 12, in the direction of arrow A, through the filter 16,to an outlet 18 downstream of the fan 15. FIGS. 2 and 3 show an inletgrille 19 a and an outlet grille 19 b, which are fitted to the inlet 17and the outlet 18 respectively formed in a housing 101 which surroundsand accommodates all of the aforementioned components of the device 10.

The particle charger 12 comprises a pin-type electrode in the form of apin 13 (represented by an arrow, the head of which points upstream torepresent the tip of the pin) mounted centrally along the length of adiametric bar 13 a (shown only in FIGS. 2 and 3) relative to acounter-electrode 14 so as to enable corona discharge from the tip ofthe pin and the generation of air ions for charging aerosol particles inthe air stream in the manner discussed earlier in this specification. Asshown clearly in FIGS. 1 and 2, the particle charger 12 and the filter16 are provided upstream of the fan 15 with significant spatialseparation or gaps, labelled G, between each of these components.

FIGS. 1 to 3 show that the device 10 undergoes two changes in itscross-sectional area between the inlet 17 and the outlet 18, in theregion of the gaps G, illustrated by the dotted lines shown joining,firstly, the particle charger 12 to the filter 16, and secondly, thefilter 16 to the fan 15. Once dirty air to be cleaned has passed throughthe particle charger 12, it experiences an expansion in cross-sectionalarea through which it can flow until it reaches the filter 16, which hasa larger cross-section (perpendicular to airflow) than the particlecharger 12. Downstream of the filter 16, cleaned air experiences acontraction in cross-sectional area through which it can flow toaccommodate the fan 15, which has a smaller cross-section (againperpendicular to airflow) than the filter 16. The changes incross-sectional area in the gaps G between the particle charger 12 andthe filter 16, and between the filter 16 and the fan 15, result inunwanted air turbulence, greater air resistance, high energy consumptionand noise.

To overcome at least one of the described mis-matches of cross-sectionalarea, it is known in the prior art to replace a single pin-typeelectrode with an array of multiple pin-type electrodes, each surroundedby an earthed counter-electrode, in order to substantially match thearea of the filter to the area of the particle charger, the fan being onthe opposite side of the filter to the particle charger (in the samemanner as is shown in FIGS. 1 to 3).

Such an arrangement is described in, for example, WO2005/102534.However, in addition to the disadvantages of the pin array electrodebeing more expensive to fabricate than a single pin-type electrode andleading to the production of more ozone as compared to a single pin-typeelectrode, the spatial separation or gaps between the three components(particle charger, filter and fan) discussed in relation to the deviceshown in FIGS. 1 to 3 still exist, and the problems of unwanted airturbulence, greater air resistance, high energy consumption, noise andthe need for tapered cowling/ducting remain. Indeed, such an array ofmultiple pin-type electrodes must be spatially separated from the filterin the device because, if placed too close to the filter, any air ionflux grounding on the filter rather than the earthed counter-electrodeof the field charger can interfere with the filter operation,significantly reducing its efficiency. Moreover, as the region betweenthe field charger and the filter is under negative pressure with respectto the ambient air when the device is in use, there is an increasedpossibility that air may bypass the pin-type electrodes, leaking intothe region separating the array from the filter. Such “charge bypass” isdetrimental as it typically leads to uncharged aerosol particles in theair entering the filter, thereby reducing particle capture efficiency.

Furthermore, a means of bridging the gaps G between the particle charger12 and filter 16, and between the filter 16 and air mover 15, isrequired: often expensive, tapered cowling or ducting must be providedto overcome the mismatch in cross-sectional areas and the spatialseparation of the components, for example in the form of housing 101. Ascan be clearly seen in FIGS. 2 and 3, the device does not exhibit 100%particle capture efficiency, or rather, the efficiency of the device 10cannot match the intrinsic efficiency of the filter 16 because of thetwo significant areas of bypass that exist with the arrangement shown.In particular, some dirty air is able to bypass the particle charger 12(“charge bypass”) as shown by arrows labelled B1 and thus, because theaerosol particles therein are not charged, they are not removed from theair stream by the filter 16. Secondly, dirty air, whether or notcontaining charged aerosol particles, is able to bypass the filter 16(“filtration bypass”) as shown by arrows labelled B2, and thus is notcleaned.

In order to achieve high efficiency of particle collection in the filter16, the charge bypass airflow around the particle charger 12 must be asmall proportion of the total air flow through the device 10. Anyaerosol particles escaping charging will tend to pass through theelectrostatic filter 18 at low efficiency. For example, in an aircleaning device operating at a particle collection efficiency above99.99% (very high efficiency), less than one part in 100,000 of thetotal air flow can be allowed to bypass the particle charger.

As mentioned earlier, the effect of such charge bypass and filtrationbypass is exacerbated when the fan 15 is located downstream of both theparticle charger 12 and the filter 16 because air is subjected to anegative air pressure compared to the surrounding atmosphere. However,because the air filter 16 is designed to be removed from the device 10for replacement or cleaning and therefore the fit between the frame ofthe filter 16 and the surrounding housing 101 is necessarily a slidingfit, filtration bypass often inevitably results. Consequently,unfiltered bypass air flow (denoted by the thinner arrows B2) is able tomix with filtered air (denoted by the thicker arrows) in a region (T) ofturbulent airflow found upstream of, and adjacent to, the fan 15, whichreduces the purity of the air (denoted by mixed thickness arrows M)issuing from the outlet 18 and outlet grille 19 b of the device 10across the entire outflow cross-sectional area, as shown in FIG. 3.

A usual arrangement of components that can be found in typical, priorart air cleaning apparatus, for example an HVAC system, are shownschematically in FIGS. 4 to 7 of the accompanying drawings.

Referring to FIGS. 4 and 5, there is shown therein a prior artelectrostatic precipitation apparatus 100 for removing unwanted aerosolparticles from an air stream. The electrostatic precipitation aircleaning apparatus 100 comprises an air mover 115 in the form of amechanical fan, a particle charger 112, and a filter 116 for removingcharged aerosol particles from the air stream (“dirty air”) (not shown)as it flows through the apparatus 100 in the volume defined by ductwork119, in the direction of arrow A, through the filter 116, to an outlet(not shown) downstream of the fan 115.

The particle charger 112 comprises an array of pin-type electrodes inthe form of an array of pins 113 mounted in a frame 113 a coupled to anarray of circular counter-electrodes 113 b formed in an adjacent plate113 c, so as to enable corona discharge from the tip of each of the pins113 and the generation of air ions for charging aerosol particles in theair stream in the manner discussed earlier in this specification. Asshown clearly in FIGS. 4 and 5, the particle charger 112 and the filter116 are provided downstream of the fan 115. Regardless of whether saidcomponents are spaced from one another or whether they are intimatelycoupled, because of an intrinsic spatial tolerance designed into each ofthe particle charger 112 and the filter 116 so as to allow each to beremovably fitted into the ductwork 119, in the absence of any specifichigh performance sealing means, such as expensive gaskets, thereinevitably exists a pathway for both charge bypass and filtration bypassaround the particle charger 112 and the filter 116 respectively.

As can be clearly seen in FIG. 5, the apparatus 100 does not exhibit100% particle capture efficiency, or rather, the efficiency of theapparatus 100 cannot match the intrinsic efficiency of the filter 116because of these two significant areas of bypass. In particular, somedirty air is able to bypass the particle charger 112 (“charge bypass”)as shown by arrows labelled B1 and thus, because the aerosol particlestherein are not charged, they are not removed from the air stream by thefilter 116. Secondly, dirty air, whether or not containing chargedaerosol particles, is able to bypass the filter 116 (“filtrationbypass”) as shown by arrows labelled B2, and thus is not cleaned.

The prior art arrangement shown in FIGS. 6 and 7 is identical to theprior art arrangement shown in FIGS. 4 and 5, except for the relativeorder of the particle charger, filter and air mover in the direction ofair flow. Thus in FIGS. 6 and 7 all like components are provided withlike reference numerals to those used in FIGS. 4 and 5, but raised by100. In particular, the particle charger 212 and the filter 216 are bothprovided upstream of the air mover 215, as compared to the direction ofair flow, defined by arrow A.

Regardless of whether said components are spaced from one another orwhether they are intimately coupled, again because of an intrinsicspatial tolerance designed into each of the particle charger 212 and thefilter 216 so as to allow each to be removably fitted into the ductwork219, in the absence of any specific high performance sealing means, suchas expensive gaskets, there inevitably exists a pathway for both chargebypass and filtration bypass around the particle charger 212 and thefilter 216 respectively.

As can be clearly seen in FIG. 7, the apparatus 200 does not exhibit100% particle capture efficiency, or rather, the efficiency of theapparatus 200 cannot match the intrinsic efficiency of the filter 216because of these two significant areas of bypass. In particular, somedirty air is able to bypass the particle charger 212 (“charge bypass”)as shown by arrows labelled B1 and thus, because the aerosol particlestherein are not charged, they are not removed from the air stream by thefilter 216. Secondly, dirty air, whether or not containing chargedaerosol particles, is able to bypass the filter 216 (“filtrationbypass”) as shown by arrows labelled B2, and thus is not cleaned.

The air cleaning efficiency of such an apparatus has been calculatedbased on the following assumptions and criteria:

Typical ductwork utilised in, for example, HVAC installations, isinevitably flexible, being fabricated from sheet metal. Measurements ofdeflection under finger-pressures in the region of 2.3 to 6.8 kg (5 to15 lbs) weight applied externally to the centre of the duct side-wallwere measured in three typical domestic HVAC installations. The chargebypass areas for each duct wall under deflection were also calculatedand expressed as a % of the total duct un-deflected area. The resultsare shown in Table 1 below.

TABLE 1 Duct Bypass Duct Duct Area Area % Width Depth (mm²) (mm²) BypassHVAC 1 Duct 1-Dimensions (mm) 254 609.6 154838.4 Duct 1-Deflection (mm)3 7 5029.2 3.25 Duct 1-Force (kg) 6.8 6.8 Duct 2-Dimensions (mm) 254 25464516 Duct 2-Deflection (mm) 5 5 2540 3.94 Duct 2-Force (kg) 6.8 6.8HVAC 2 Duct 1-Dimensions (mm) 254 254 64516 Duct 1-Deflection (mm) 3 52032 3.15 Duct 1-Force (kg) 4.5 4.5 Duct 2-Dimensions (mm) 254 254 64516Duct 2-Deflection (mm) 5 6 2794 4.33 Duct 2-Force (kg) 6.8 6.8 HVAC 3Duct 1-Dimensions (mm) 254 254 64516 Duct 1-Deflection (mm) 5 5 25403.94 Duct 1-Force (kg) 4.5 4.5 Duct 2-Dimensions (mm) 254 254 64516 Duct2-Deflection (mm) 5 7 3048 4.72 Duct 2-Force (kg) 2.3 4.5 Duct3-Dimensions (mm) 254 254 64516 Duct 3-Deflection (mm) 7 3 2540 3.94Duct 3-Force (kg) 4.5 6.8

It can be seen that the resulting deflections were in the range of 3 mmto 7 mm. Taking each deflection and assuming an average bypass gap alongeach frame length of 50% of the deflection, the resulting bypass areafor four sides of the entire rectangular duct when compared to the totalcross-sectional area can be calculated.

Assuming that the air flow distributes proportionally to the crosssectional areas of the bypass and un-deflected duct, the bypass flowaverages 3.9% over the examples above. This represents a bypass of 3,900parts per 100,000 of total air flow and would reduce the maximumachievable efficiency to 96.1%, which is far lower than desired.

Ductwork can, of course, be strengthened with ribs and brackets or evenby the insertion of a purpose made cabinet, however such modificationsare difficult and expensive, and still require high quality sealingaround the particle charger frame to the interior walls of thesurrounding duct.

It is an object of the present invention to obviate or mitigate some, orpreferably all, of the abovementioned disadvantages, particularly inrelation to charge bypass.

Furthermore, there is a need for a personal air cleaner (air cleaningdevice) which can deliver pure air, essentially free of all particles,(meaning a typical air cleaning efficiency of 99.9%), directly into theimmediate breathable atmosphere of a user. It is known that someindividuals have a great sensitivity to aerosol particles (includingdust particles and other allergens) and suffer ill-health when exposedto certain types of particle. For example, a single pollen particle canin some individuals trigger a severe allergic response. With an aircleaner designed to deliver pure air with a 99.9% particle removalefficiency, at the air cleaner outlet, a user can gain the full benefitsof breathing contaminant-particle-free air.

It is therefore a further object of the present invention to eliminatethe disadvantages of previous air cleaners, particularly personal aircleaners.

According to a first aspect of the present invention there is providedan air cleaning device for removing aerosol particles from an airstream, the device comprising:

-   (a) a particle charger comprising a housing and an electrode    arrangement therein for generating air ions in the air stream, the    particle charger having a particle charging zone within which, in    use, aerosol particles in the air stream are electrically charged    via collision with the air ions;-   (b) a filter for precipitating electrically charged aerosol    particles from the air stream moving through the device; and-   (c) an air mover, comprising a casing, for moving the air stream    through the device;

wherein the particle charger and the air mover are provided upstream ofthe filter; and

wherein the housing of the particle charger is hermetically sealed tothe casing of the air mover in the direction of air flow through thedevice, such that the particle charger and the air mover are intimatelycoupled together, whereby all air entering the device has to passthrough both the particle charger and the air mover.

Such a device ensures that charge bypass is eliminated because ALL ofthe air entering the device MUST pass through the particle chargingzone, meaning all aerosol particles in the air stream must also passthrough the particle charging zone, where electrical charging viacollision with air ions occurs. This is made possible because thehousing of the particle charger and the casing of the air mover togetherdefine the volume through which the air stream must flow in order topass through the filter—no additional surrounding housing, cowling orductwork is required. Furthermore, with such a device, pure air with a99.9% particle removal efficiency, can be delivered at the deviceoutlet, such that a user can gain the full benefits of breathingcontaminant-particle-free air.

For the avoidance of any doubt, reference to the housing of the particlecharger being hermetically sealed to the casing of the air mover “in thedirection of air flow through the device” indicates the sequence of thehermetic seal between the particle charger and the air mover; in otherwords, when viewed in the direction of air flow through the device,either the particle charger is hermetically sealed to, and is locatedupstream of, the air mover, or, the particle charger is hermeticallysealed to, and is located downstream of, the air mover.

Said device is preferably portable and thus can function as a standaloneair cleaner.

According to a second aspect of the present invention there is providedan alternative air cleaning device for removing aerosol particles froman air stream, the device comprising:

-   (a) an air mover, comprising a casing, for moving the air stream    through the device, wherein the casing has an air inlet portion and    an air outlet portion, either one of which comprises a first part of    an electrode arrangement for generating air ions in the air stream;-   (b) a particle charger comprising a second part of the electrode    arrangement for generating air ions in the air stream, wherein,    together, the particle charger and whichever one of the air inlet    portion and the air outlet portion of the casing of the air mover    that comprises the first part of the electrode arrangement define a    particle charging zone within which, in use, aerosol particles in    the air stream are electrically charged via collision with the air    ions; and-   (c) a filter for precipitating electrically charged aerosol    particles from the air stream moving through the device;

wherein the particle charger and the air mover are provided upstream ofthe filter; and

wherein the particle charger is accommodated by, and hermetically sealedto, the air inlet/outlet portion of the casing of the air mover in thedirection of air flow through the device, such that the particle chargerand the air mover are intimately coupled together, whereby all airentering the device has to pass through both the particle charger andthe air mover.

Again, such a device ensures that charge bypass is eliminated becauseALL of the air entering the device MUST pass through the particlecharging zone, meaning all aerosol particles in the air stream must alsopass through the particle charging zone, where electrical charging viacollision with air ions occurs. This is made possible because the airinlet/outlet portion of the air mover, within which the particle chargeris accommodated, defines the volume through which the air stream mustflow in order to pass through the filter—no additional surroundinghousing, cowling or ductwork is required.

For the avoidance of any doubt, reference to the particle charger beingaccommodated by, and hermetically sealed to, the air inlet/outletportion of the air mover “in the direction of air flow through thedevice” indicates the sequence of the hermetic seal between the particlecharger and the air mover; in other words, when viewed in the directionof air flow through the device, either the particle charger ishermetically sealed to, and is located at the upstream end of, the airmover, or, the particle charger is hermetically sealed to, and islocated at the downstream end of, the air mover.

According to a third aspect of the present invention there is providedan air cleaning apparatus for removing aerosol particles from an airstream, the apparatus comprising:

-   (a) a housing comprising a first part of an electrode arrangement    for generating air ions in the air stream;-   (b) a particle charger, located in the housing, and comprising a    second part of the electrode arrangement for generating air ions in    the air stream, wherein, together, the particle charger and the    housing define a particle charging zone within which, in use,    aerosol particles in the air stream are electrically charged via    collision with the air ions;-   (c) a filter, located in the housing, for precipitating electrically    charged aerosol particles from the air stream moving through the    apparatus; and-   (d) an air mover, located in the housing, for moving the air stream    through the apparatus;

wherein the particle charger and the air mover are provided upstream ofthe filter; and

wherein the housing provides a hermetic seal between the particlecharger and the air mover in the direction of air flow through theapparatus, such that the particle charger and the air mover areintimately coupled together, whereby all air entering the apparatus hasto pass through both the particle charger and the air mover.

Such an apparatus ensures that charge bypass is eliminated because allof the air entering the apparatus must pass through the particlecharging zone, meaning all aerosol particles in the air stream must alsopass through the particle charging zone, where electrical charging viacollision with air ions occurs. This is made possible because thehousing of the apparatus, the particle charger and the air movertogether define the volume through which the air stream must flow inorder to pass through the filter—no additional surrounding housing,cowling or ductwork is required.

For the avoidance of any doubt, reference to the housing providing ahermetic seal between the particle charger and the air mover “in thedirection of air flow through the apparatus” indicates the sequence ofthe hermetic seal between the particle charger and the air mover; inother words, when viewed in the direction of air flow through thedevice, either the particle charger is hermetically sealed to, and islocated upstream of, the air mover, or, the particle charger ishermetically sealed to, and is located downstream of, the air mover. Ineach of the aforementioned aspects of the invention, the particlecharger and the air mover may be intimately coupled, i.e. hermeticallysealed, as particle charger/air mover in the direction of air flow (suchthat the particle charger is upstream of the air mover) or as airmover/particle charger (such that the air mover is upstream of theparticle charger)—in both instances, the “couple” is upstream of thefilter.

In the air cleaning device according to the first aspect of theinvention, the housing of the particle charger has an inlet and anoutlet, and the casing of the air mover has an inlet and an outlet, suchthat the intimate couple may be achieved by a hermetic seal of theoutlet of the housing of the particle charger to the inlet of the casingof the air mover, or, it may be achieved by a hermetic seal of theoutlet of the casing of the air mover to the inlet of the housing of theparticle charger. This is achieved in practice by provided said “sealingparts” with a common cross-sectional area with a high degree of accuracy(of the order of ±0.127 to 0.508 mm (±5 to 20 thousandths of an inch)).Although cylindrical, or substantially cylindrical, commoncross-sectional areas may be preferred, it is within the scope of theinvention for the common cross-sectional area to be of any shape, e.g.oval or polygonal, such as octagonal or hexagonal.

In the air cleaning device according to the second aspect of theinvention, the air mover has an air inlet portion and an air outletportion, within either one of which the particle charger may beintimately coupled, by means of a hermetic seal.

In the air cleaning apparatus of the third aspect of the invention, thehousing accommodates all of the components, such that the particlecharging zone defined by it and the particle charger is effectivelyhermetically sealed to the air mover, whether the air mover is providedupstream or downstream of the particle charger.

In use, air flowing through the air cleaning device and air cleaningapparatus flows along an air stream passage and through a volume from anair inlet of the device or apparatus to an air outlet of the device orapparatus. The air inlet of the device/apparatus may be provided at theinlet end of the intimate couple, i.e. at whichever of the particlecharger and air mover is upstream in the couple. The air outlet of thedevice/apparatus may be provided at the downstream end of the filter.

Throughout this specification, when a first component is described asbeing “upstream” of a second component, it is intended to mean that thefirst component is provided further towards the air inlet of thedevice/apparatus than the second component. Put another way, in use, airwill flow past a first component before a second component if the firstcomponent is upstream of the second component. The term “downstream”should be construed accordingly.

A further advantage of the present invention resides in the alteredpositioning of components relative to one another as compared to theconventional ordering of such components. In particular, in relation tothe first and third aspects of the invention, since both the particlecharger and the air mover are provided upstream of the filter, it ispossible to reduce the number of changes in cross-sectional area of theair stream to one, or potentially eliminate changes in cross-sectionaltogether.

As a result of both the intimate coupling of the particle charger andthe air mover with the unconventional ordering of the componentsdiscussed above, the present invention may ameliorate or mitigate theaforementioned disadvantages in terms of turbulence, higher airresistance, greater energy consumption, noise, and in particular theproblem of charge bypass or leakage. By extension, it may also remove orreduce what appears to be an industry bias against using pin-typeemission electrodes (as opposed to wire array emission electrodes) infield chargers used in air cleaning devices. This may ameliorate issueswith ozone generation and the deposition of substances on the wireemission electrodes observed when wire arrays are used in fieldchargers, while providing for a higher efficiency of particle chargingper unit of corona current in a pin-type emission electrode as comparedwith that achievable with a wire array electrode (for a given appliedcurrent).

Any suitable filter for capturing charged aerosol particles may be usedin an air cleaning device of the invention. In one preferred embodiment,the filter may be an electrostatic filter, which operates by using anelectric field to deflect charged aerosol particles passing therethroughin order to cause those particles to be precipitated onto a filtersurface. In another preferred embodiment the filter may be an electretfilter. In yet another preferred embodiment of the invention, the filtermay be an electrostatic precipitator. Such filters are well known tothose of skill in the art.

As described in International patent publication WO00/61293, forexample, an electrostatic filter can comprise an array of passages whichforms part of the fluid passage through the electrostatic precipitationdevice and through which a gas stream can pass relatively freely (thepassages being provided between plastics walls and the plastics wallshaving areas of conductive material in contact therewith), and means forapplying high and low electrical potentials alternately to isolatedareas of the conductive material to provide charged sites in the arrayfor collecting particles from the gas stream. Use of this particulartype of filter with the air cleaning device of the first aspect of theinvention may provide particular benefits in that such a filter tends tocollimate the air flow therethrough, thus maximising the availability oflaminar air flow exiting the device to a user, with any air that hasbeen subject to filtration bypass being confined to the peripheralregion of the overall flow of air exiting the device, such that it doesnot mix and contaminate purified air exiting the filter.

An electret filter may comprise an array of layers of fluted plasticssheet material or it may be formed of fibrous media, in which the fibresmay be charged by electrodes in the filter or during manufacture of thefilter.

Alternative configurations for the filter component are well known tothose of skill in the art and any appropriate filter may form part of anelectrostatic precipitation air cleaning device according to the presentinvention.

The air mover may take the form of any conventional component well knownto those of skill in the art for effecting urging (or movement) of airin a desired direction. The air mover may, for example, take the form ofa mechanical fan, bellows or a convective airflow device. Such an airmover is particularly useful in the first and third aspects of theinvention. Alternatively, the air mover may take the form of acentrifugal fan, also known as a “blower”. Such an air mover isparticularly useful in the second aspect of the invention. Many othersuitable components would be well known to those of skill in the art andany appropriate air mover may form part of an electrostaticprecipitation air cleaning device according to the present invention.

The electrode arrangement comprised in each of the air cleaning devicesand the air cleaning apparatus according to the invention comprises twoparts: an electrode and a counter-electrode. In the air cleaning deviceof the first aspect, the particle charger comprises both the electrodeand the counter-electrode. In the air cleaning device of the secondaspect, the first part of the electrode arrangement comprised in the airinlet/outlet portion of the casing of the air mover preferably may bethe counter-electrode, whilst the second part of the electrodearrangement comprised in the particle charger preferably may be theelectrode. In the air cleaning apparatus of the third aspect, the firstpart of the electrode arrangement comprised in the housing preferablymay be the counter-electrode, whilst the second part of the electrodearrangement preferably may be the electrode.

The electrode may be in the form of a pin or elongate wire—each having atip or end—and may be supported on a support rod, which may additionallybe conductive. Two or more electrodes may be supported on a support rod.In all cases, the electrode is capable of corona discharge, as describedearlier in this specification. The counter-electrode (non-corona) may beconfigured to be operable at a different electrical potential to that ofthe (corona) electrode in the electrode arrangement. In both the deviceand the apparatus, the counter-electrode will surround the tip/end ofthe electrode but will be separated therefrom by a clearance. Thecounter-electrode may be earthed. Provision of a counter-electrodeprovides a potential gradient of sufficient strength to ignite thecorona discharge required to generate air ions. Furthermore, theresulting electric field accelerates the air ions generated so that theycross the space in the field charger through which air to be cleaned(containing unwanted aerosol particles) passes; as said aerosolparticles collide with air ions, charge is transferred from the air ionsto the aerosol particles, thus enabling subsequent collection of theaerosol particles by the filter.

The counter-electrode may be shaped such that the distance from thetip/end of the electrode to the surface of the surroundingcounter-electrode is approximately constant around the periphery of thetip/end; the air ion flux generated at the tip/end will thus besubstantially symmetrical and radial, ensuring that a very highproportion (99.99% is regularly achievable) of the unwanted aerosolparticles in the air collide with air ions, leading to the desiredcharge transfer and subsequent particle capture.

In the air cleaning device of the first aspect of the invention, thecounter-electrode may comprise a conductive plate (preferably, but notnecessarily, a substantially flat plate) having an aperture therein.Alternatively, the counter-electrode may comprise a hollow cylinder,which may be formed of a conductive material, or which may be providedwith a conductive interior surface. The aperture in the plate or thecross-section of the cylinder may be rectangular, square, circular orelliptical, and will have a central longitudinal axis extendingorthogonal to the plate or co-extensive with the cylinder. In any ofthese embodiments, the tip/end of the electrode preferably liessubstantially co-axial with the axis of the aperture/cylinder, and ispreferably centrally disposed within the aperture in the plate or withinthe cylinder to ensure that the clearance is approximately constantaround the periphery of the tip/end of the electrode.

More preferably, the counter-electrode of the air cleaning device of thefirst and second aspects of the invention may be generally annular, i.e.the aperture in the conductive plate may be circular or the hollowcylinder may have a circular cross-section. Most preferably, in thefirst aspect of the invention, the housing of the particle charger ofthe air cleaning device may comprise the counter-electrode, oralternatively, may form the counter-electrode. An interior surface ofthe housing of the particle charger, preferably an interior surfaceadjacent to the electrode, may be provided with an electricallyconductive coating or layer which functions as the counter-electrode.Alternatively, the housing may be formed of a suitably electricallyconductive material, suitably insulated from external components. Thetip/end of the electrode may be substantially concentric with thecounter-electrode. In the second aspect of the invention, particularlywhen the air mover takes the form of a blower having an air intake andan air outlet perpendicular to the intake, the (corona) emissionelectrode may be provided in the air intake of the blower. Thecounter-electrode (non-corona) may also be located in the air intake ofthe blower. In such an embodiment, the air intake may comprise aconductive portion, e.g. a conductive ring or a conductive interiorsurface, forming the counter-electrode. Location of thecounter-electrode in this way facilitates a particularly compact designof the device of the present invention. Such location is made possiblesince the filter component is not located in between the air mover andparticle charger, and indeed will often be external of, and remote to,the blower.

In the air cleaning apparatus, the housing may be in the form of aducting or ductwork which may comprise the counter-electrode, oralternatively, may form the counter-electrode. An interior surface ofthe housing of the apparatus, preferably an interior surface adjacent tothe electrode of the particle charger, may be provided with anelectrically conductive coating or layer which functions as thecounter-electrode. Alternatively, the housing of the apparatus may beformed of a suitably electrically conductive material, suitablyinsulated from external components. The tip/end of the electrode may besubstantially co-axial with a longitudinal axis of the housing of theapparatus, i.e. with the longitudinal axis of the ductwork which extendsin the overall direction of air flow.

The conductive interior surface of the counter-electrode as describedherein as an option may be comprised of a conductive ink or paint.Conductive inks and paints offer a convenient way to apply acounter-electrode to otherwise non-conductive surfaces.

A device according to the first aspect of the invention may comprise twoor more air movers and/or two or more particle chargers, each of thelatter having an electrode arrangement for generating air ions in theair stream, i.e. two or more intimate couples in which the housing ofone particle charger is hermetically sealed to the casing of one airmover, which may be provided in a side-by-side arrangement so as toeffectively double the cross-sectional area available for air to becleaned to move through. In such an arrangement, the two (or more)intimate couples may be used with a common filter, or with a filtereach.

According to a fourth aspect of the present invention there is provideda method of removing aerosol particles from an air stream andeliminating charge bypass, the method comprising:

generating air ions in the air stream using a particle chargercomprising a housing and an electrode arrangement therein;

electrically charging aerosol particles in the air stream via theircollision with air ions in a particle charging zone of the particlecharger; and

moving the air stream towards a filter using an air mover comprising acasing, whereby electrically charged aerosol particles in the air streamare precipitated onto the filter,

wherein the housing of the particle charger is hermetically sealed tothe casing of the air mover in the direction of air flow, such that theair stream is moved through an intimate couple of the particle chargerand the air mover, whereby all air to be cleaned has to pass throughboth the particle charger and the air mover, prior to its arrival at thefilter.

The method of the fourth aspect of the invention is preferably achievedusing an air cleaning device according to the first aspect of theinvention.

According to a fifth aspect of the present invention there is provided amethod of removing aerosol particles from an air stream and eliminatingcharge bypass, the method comprising:

generating air ions in the air stream using a housing comprising a firstpart of an electrode arrangement and a particle charger, located in thehousing, comprising a second part of the electrode arrangement;

electrically charging aerosol particles in the air stream via theircollision with air ions in a particle charging zone defined by theparticle charger together with the housing; and

moving the air stream towards a filter, located in the housing, using anair mover comprising a casing, located in the housing, wherebyelectrically charged aerosol particles in the air stream areprecipitated onto the filter,

wherein the housing provides a hermetic seal between the particlecharger and the air mover in the direction of air flow, such that theair stream is moved through an intimate couple of the particle chargerand the air mover, whereby all air to be cleaned has to pass throughboth the particle charger and the air mover, prior to its arrival at thefilter.

The method of the fifth aspect of the invention is preferably achievedusing an air cleaning apparatus according to the third aspect of theinvention.

Preferred features described above in relation to the first and secondaspects of the present invention also represent preferred features ofthe above third and fourth aspects of the present invention subject to atechnical incompatibility that would prevent such a combination ofpreferred features. Furthermore, it will be evident to the skilledperson that advantages set out above in respect of the first and secondaspects of the present invention are also offered by the third andfourth aspects of the present invention.

For the avoidance of any doubt, it should be noted that various featuresof the invention discussed above may be used in combination, subject toa technical incompatibility that would prevent such a combination ofpreferred features. So, for example, in a specific embodiment of thepresent invention, the air mover is in the form of a blower andcomprises a cylindrical intake formed of conductive material, theconductive material being earthed and forming a circularcounter-electrode for the particle charger. In this embodiment, thetip/end of the emission electrode may be provided co-axially within thecylindrical intake, but separated from the counter-electrode by aclearance.

The invention will now be further described, by way of example only,with reference to the accompanying drawings (not to scale), in which:

FIGS. 1 to 3 are schematic side cross sections of a prior artelectrostatic precipitation device, discussed earlier in thisspecification;

FIGS. 4 and 6 are schematic perspective views of two alternative priorart electrostatic precipitation apparatus, discussed earlier in thisspecification;

FIGS. 5 and 7 are schematic side cross-sections of each of the twoalternative prior art electrostatic precipitation apparatuses shown inFIGS. 4 and 6 respectively;

FIGS. 8 and 9 are schematic side cross sections of an embodiment of anelectrostatic precipitation air cleaning device according to the presentinvention;

FIGS. 10, 11 and 12 are schematic side cross sections of a secondembodiment of an electrostatic precipitation air cleaning deviceaccording to the present invention;

FIGS. 13 and 14 are schematic side cross sections of a third embodimentof an electrostatic precipitation air cleaning device according to thepresent invention;

FIGS. 15 and 16 are schematic perspective views of a fourth embodimentof an electrostatic precipitation air cleaning device according to thepresent invention;

FIG. 17 is a schematic perspective view of an embodiment of anelectrostatic precipitation apparatus according to the invention; and

FIG. 18 is a schematic cross-section of the electrostatic precipitationapparatus shown in FIG. 17.

Referring to FIGS. 8 and 9, both of which illustrate a first embodimentof the invention, there is shown an electrostatic precipitation aircleaning device 20 for removing unwanted aerosol particles from an airstream. In a similar manner to the prior art device 10 shown in FIGS. 1to 3, the air cleaning device 20 of FIGS. 8 and 9 comprises a particlecharger 22, an air mover 25 in the form of a mechanical fan, and afilter 26 for removing charged aerosol particles from the air stream(not shown) as it flows through the device 20.

The particle charger 22 comprises a cylindrical housing 22 a having anelectrode arrangement therein for generating air ions in the air stream.The housing 22 a is open at each of its airflow ends 22 b, 22 c so as toallow the air stream to pass through. The electrode arrangementcomprises an electrode 23 in the form of a pin (represented by an arrow,the head of which points upstream to represent the tip of the pin)mounted centrally (lengthways) on a diametric bar 23 a mounted in thehousing 22 a, and a counter-electrode 24 in the form of an annularconductive coating provided on the interior surface of the housing 22 a,surrounding the electrode 23 in a concentric manner. A particle chargingzone is the volume defined by the extent of electrical communicationbetween the electrode 23 and counter-electrode 24 within which, in use,aerosol particles in the air stream are electrically charged viacollision with the air ions.

The air mover 25 comprises a cylindrical casing 25 a within which fanblades 25 b are mounted (only two of which are shown for clarity). Thecylindrical casing 25 a of the fan 25 and the cylindrical housing 22 aof the particle charger 22 are both made of a material that can bemachined, injection-moulded or otherwise formed to a high dimensionalprecision, e.g. a plastics material such as PVC or a die-cast metal. Thecylindrical casing 25 a of the fan 25 is hermetically sealed to thecylindrical housing 22 a of the particle charger 22 in the direction ofair flow, whereby all air entering the device 20 has to pass throughboth the particle charger 22 and the air mover 25, such that chargebypass is eliminated.

Unlike the device 10 shown in FIGS. 1 to 3, the order of the componentsand the relative spatial orientation of the components in the device 20shown in FIGS. 8 and 9 is quite different: the particle charger 22 andthe fan 25 are joined together in an airtight manner as an intimatecouple 29, with the particle charger 22 being upstream of the fan 25.The air stream flows via an inlet 27 at the entrance to the particlecharger 22, in the direction of arrow A, through the intimate couple 29of particle charger 22 and fan 25, to the filter 26 via a gap, G,(illustrated by the dotted lines) therebetween and on to an outlet 28.In practice, this gap, G, would be contained by tapered cowling 21 orother such suitable ducting, as shown in FIG. 9.

In the device 20 in FIGS. 8 and 9, the particle charger 22 comprises apin (corona) electrode 23, which is mounted centrally relative to asurrounding counter-electrode 24 so as to enable corona discharge fromthe tip of the pin and the generation of air ions for charging aerosolparticles in the air stream in the manner discussed earlier in thisspecification.

As shown clearly in FIGS. 8 and 9, the particle charger 22 and the fan25 are joined together in an airtight manner (a hermetic seal is formed)forming the intimate couple 29 upstream of the filter 26; there is nogap between the particle charger 22 and the fan 25, and although a gap,G, is shown as being present between the intimate couple 29 and thefilter 26, it is under positive pressure with respect to ambient air andthus any bypass or leakage into the gap, G, (as a result of anyimperfection in the cowling 21) of uncharged aerosol particles to thefilter 26 is minimised, if not also completely eliminated.

In other words, unlike the prior art device 10 shown in FIGS. 1 to 3,the air stream passageway in the device 20 in FIGS. 8 and 9 undergoesonly a single change in cross-sectional area (perpendicular to thedirection of air flow) from the inlet 27 to the outlet 28. Thepassageway is relatively narrow (i.e. has a small cross-sectional area)at the inlet 27 of the device 20 to ensure that substantially all of theaerosol particles in the air flowing therethrough encounter air ions forcharge transfer. Downstream of the particle charger 22 is provided thefan 25, and the passageway remains substantially constant incross-section from the particle charger 22 to the fan 25, assistingformation of the intimate couple 29. Downstream of the fan 25, thepassageway undergoes an expansion in cross-sectional area to accommodatethe relatively large filter 26.

As there is only a single change in cross-sectional area of the airstream passageway, air passing through the device 20 in FIGS. 8 and 9encounters less turbulence, air resistance, requires less energy andproduces less noise; and the need for relatively costly cowling/ductingrequired to match the different cross sections as compared with theprior art device 1 in FIGS. 1 to 3 (which comprises two changes in crosssectional area of the gas passageway) is reduced.

The intimate couple of the particle charger 22 and the fan 25 is coupledto the filter 26 by means of cowling 21, which extends from an outlet ofthe fan casing 25 a to the filter 26. Further external structure of thedevice 20, which is unimportant to the functioning components describedabove, is indicated schematically by the dotted lines shown in FIG. 9.

Referring now to FIGS. 10, 11 and 12, there is shown therein a secondembodiment of an electrostatic precipitation air cleaning device 30 inaccordance with the present invention for removing aerosol particlesfrom an air stream. The device 30 of the second embodiment is similar tothe first embodiment shown in FIGS. 8 and 9, and only the differencesbetween the devices 20, 30 will be described in detail below. In FIGS.10, 11 and 12, the components corresponding to those described above inrelation to FIGS. 8 and 9 take the reference numbers used in FIGS. 8 and9 but raised by 10.

Unlike the device 20 in FIGS. 8 and 9, because the filter 36 is sizedsuch that its cross-section is the same as the cross-sectional area ofthe intimate couple 39 (formed by joining in an airtight manner of theparticle charger 32 and the air mover in the form of a fan 35, such thatthe housing of the former is hermetically sealed to the casing of thelatter), the air stream passageway in the device 30 in FIGS. 10, 11 and12 undergoes no change in cross-sectional area from the inlet 37 to theoutlet 38. As there is no change in cross-sectional area, air flowingthrough the device in FIGS. 10, 11 and 12 encounters less turbulence,air resistance, requires less energy and produces less noise; and thereis no need for any relatively costly cowling/ducting to match differentcross-sections as compared with the prior art device 10 shown in FIGS. 1to 3 and with the device 20 according to the invention shown in FIGS. 8and 9. Charge bypass is eliminated, filtration bypass and/or leakage isalso reduced and particle charging efficiency and therefore capture isincreased over and above that already achieved with the embodiment ofthe invention shown in FIGS. 8 and 9.

FIG. 12 shows a particular effect achievable with the present inventionwhen charge bypass is eliminated, even though there may still be anamount of filtration bypass (because air filters must be designed to beremoved from an air cleaner for replacement or cleaning and thereforethe fit between the filter frame and the surrounding housing or ductworkis necessarily a sliding fit with inevitable bypass). Air is drawnthrough the particle charging zone such that charging of aerosolparticles therein occurs. After passing through the fan 35, the air isin a positive pressure region and is blown through the filter 36 (andoutlet grille, not shown) to produce a smooth laminar flow of air,represented by arrow L, which is of particular use when it can bedirected toward the face of the user. The effect is particularlypronounced when the filter 36 is an electrostatic filter, such as isdescribed in International patent publication WO00/61293. All of thecharged particles passing through the filter are filtered out, and ifthere is any small leakage of bypass air (shown by arrows B) around thesides of the filter 36, this is not mixed with, and does not impact thelaminar flow of, air exiting the filter 36. The user is subject to thefull benefits of the particle-free air issuing from the filter 36. Suchan effect is in direct contrast to most prior art portable air cleaners,such as is exemplified in FIGS. 1 to 3, which are designed with the fandownstream of the filtration means (whether that be an ion charger andfilter combination or solely a filter). This results in the filtrationmeans being under negative pressure with respect to the ambient air,which means that uncharged, unfiltered air (bypass air) is drawn throughgaps or joints into the air cleaner at any or all of the couplingpoints. Bypass air (for example originating from around the removablefilter) is drawn into the turbulent (negative pressure) regiondownstream of the fan where it is mixed with the clean air being drawnthrough the filter. Air blown out by the fan, in this common design ofprior art air cleaner, is often at high velocity, is non laminar, isuncomfortable when blown at a personal user and is contaminated by thisunfiltered air. Overall particle removal efficiency as measured betweenair into the air cleaner and out of the fan is often significantlyreduced. The embodiment of the invention shown in FIGS. 10, 11 and 12overcomes these prior art disadvantages.

Referring now to FIGS. 13 and 14, there is shown therein a furtherelectrostatic precipitation air cleaning device 40 in accordance withthe present invention for removing aerosol particles from an air stream.The device 40 of the third embodiment is effectively a stack of three ofthe devices 30 shown in FIGS. 10, 11 and 12, and as such the samereference numbers as those used to describe FIGS. 10, 11 and 12 will beused in FIGS. 13 and 14.

Three particle chargers 32, each having a pin electrode 33, and threeair movers in the form of mechanical fans 35 are provided upstream of asingle filter 36 in the device in FIGS. 13 and 14 (cf one of eachrespective component in the devices 20, 30 in FIGS. 8 and 9, and FIGS.10, 11 and 12), i.e. three intimate couples 39 are provided upstream ofthe single filter 36. The presence of a single filter, spanning thethree intimate couples 39, rather than three separate filters (one percouple) is the only modification made as compared to an exact stack ofthree of the devices 30 shown in FIGS. 10, 11 and 12. Of course, theembodiment shown in FIGS. 13 and 14 could be so modified such that thefilter 36 spanned just two of the intimate couples 39 (with the thirdcouple being provided with its own filter), or such that each intimatecouple is provided with its own filter. All of these combinations arewithin the scope of the present invention.

The three particle chargers 32 are provided in the air stream passagewayin a side-by-side arrangement (in this case, stacked one on top of theother), such that air flowing through the device encounters one or theother two particle chargers 32. Similarly, the three fans 35 are alsoprovided in a side-by-side arrangement (again stacked one on top of theother and each being substantially co-axial with a respective particlecharger 32), such that air flowing through the device 40 is drawnthrough one or the other two fans 35.

In use, some air flowing through the air stream passageway flows throughthe uppermost particle charger 32 and uppermost fan 35 to the commonfilter 36, some through the middle particle charger 32 and middle fan tothe common filter 36, and some through the lowermost particle charger 32and the lowermost fan 35 to the common filter 36.

Each of the three particle chargers 32 has a similar cross-sectionalarea to each of the three fans 35, and so the total air streampassageway therebetween remains substantially constant incross-sectional area. The collective cross-sectional area of the threeparticle chargers 32 and three fans 35 is similar to that of the singlefilter 36, (i.e. the filter 36 has a cross-sectional area approximatelythree times that of each intimate couple 39). Because of the similarityin cross-sectional area, the air stream passageway between the fans 35and the filter 36 remains substantially constant in cross-section.

In light of the above, as with the device in FIGS. 10, 11 and 12, theair stream passageway in the device in FIGS. 13 and 14 undergoessubstantially no change in cross-sectional area from its inlets 37 toits outlets 38. As there is substantially no change in cross-sectionalarea, air passing through the device 40 in FIGS. 13 and 14 encountersless turbulence, air resistance, requires less energy and produces lessnoise; there is no need for relatively costly connecting tubes requiredto match the different cross sections as compared with the devices 20,30 in FIGS. 8 and 9, and 10, 11 and 12. As shown, the common filter 36is fitted to the downstream end of the three intimate couples 39 bymeans of a straightforward housing (not shown). Thus charge by[pass iseliminated, filtration bypass and/or leakage is also reduced andparticle charging efficiency and therefore capture is increased over andabove that already achieved with the embodiment of the invention shownin FIGS. 8 and 9.

Referring now to FIGS. 15 and 16, there is shown therein a furtherelectrostatic precipitation air cleaning device 50 in accordance withthe invention for removing aerosol particles from an air stream. Thedevice 50 comprises a particle charger 52, an air mover 55 in the formof a blower, and a filter, which although not explicitly shown here,would be positioned downstream of the air flow exiting the blower 55,which air flow is labelled with arrow F.

The particle charger 52 and the blower 55 are joined together(hermetically sealed together) in an airtight manner as an intimatecouple 59, with the particle charger 52 being upstream of the blower 55.The air stream flows via an inlet 57 at the entrance to the particlecharger 52, through the intimate couple 59 of particle charger 52 andblower 55, to the filter (somewhere downstream of air flow shown byarrow F) and on to an outlet (not shown). In practice, cowling or othersuch suitable ducting would be provided to position the filterexternally of the blower 55.

More specifically in FIGS. 15 and 16, the particle charger 52 comprisesa pin (corona) electrode 53 mounted centrally on a diametric rod 53 awhich is mounted in an intake (air inlet section) 51 of the blower 55.The intake 51 is conductive and earthed, and as a result the intake 51behaves as a counter-electrode (also referenced as 54 hereinafter) forthe pin electrode 53, thereby improving particle charging effectiveness.The intake 51 is shown as a protruding member in FIG. 5, however itcould easily be in the form of an opening in the otherwise flat outersurface of the side of the blower 55. The intake 51, whether in the formof a protrusion (as shown) or a flush opening (as an alternative) canitself be conductive (as described above) or, if formed of anon-conductive material, e.g. a plastics material, be provided with aconductive interior surface, e.g. an area, preferably a ring, ofconductive ink or paint to form the counter-electrode. The intake 51 ofthe blower 55 is substantially cylindrical, meaning that thecounter-electrode 54 is similarly cylindrical, whereas the tip of thepin electrode 53 is substantially a point. The cylindricalcounter-electrode 54 and tip of the pin electrode 53 are, therefore,symmetrically arranged, which means, in combination with the pinelectrode 53 and the counter-electrode 54 being concentric, that thedistance from the pin tip to the inner surface of the surroundingelectrode is approximately constant. This means that the air ion fluxbetween the pin electrode 53 and the surrounding counter-electrode 54 isradial, thereby increasing the likelihood of air ion-aerosol particlecollisions, which further improves particle charging effectiveness bythe corona electrode 53 and eliminates charge bypass.

Test Data

An electrostatic air precipitation device, of the type schematicallyshown in FIGS. 10, 11 and 12 of the accompanying drawings, was testedfor its aerosol particle capture efficiency by varying the currentsupplied to the pin emission electrode of the particle charger as afunction of captured particle size. Air flow to the device wascontrolled at 1.2 metres per second filter face velocity for all tests.The filter used was an electrostatic, fluted “ifD filter” of 3 inches(76.2 mm) depth supplied by Darwin Technology International Limited(www.tfdair.com); the ifD filter was operated at 10 kV between adjacentelectrodes. The number of particles was measured using a laser particlecounter (Lighthouse Handheld Model No. 3016) which was operatedconsistently so that a % particle capture efficiency could becalculated. The results are shown in Table 2 below.

TABLE 2 Current Supplied Captured Particle Size (μm) (μA) 0.3 0.5 0.71.0 2.0 5.0 1.0 99.35 99.46 99.26 99.59 99.03 100.00 2.0 99.88 99.9299.94 99.88 100.00 100.00 3.0 99.95 100.00 100.00 100.00 100.00 100.004.0 99.99 100.00 100.00 100.00 100.00 100.00 5.0 100.00 100.00 100.00100.00 100.00 100.00

The percentage particle capture efficiencies noted in Table 2 aboveclearly show a general trend of increasing efficiency with increasedcurrent supplied, for each of the particle sizes captured, andincreasing efficiency with which increasingly large particles arecaptured for a given current supplied (subject to experimental error).

Larger aerosol particles are generally easier to capture than smallerparticles (due in part to there being a greater likelihood of collisionof larger particles with air ions and thus more charged particles tocapture). However, even with aerosol particle sizes as small as 0.3 μm,with only 1.0 pA of current supplied to the pin-type electrode, greaterthan 99% (99.35%) efficiency is achieved, this rising to 99.99% with 4.0pA of current supplied.

It should of course be noted that all of the efficiencies quoted aresubject to the operational measurement limitations of the particlecounter.

Referring now to FIGS. 17 and 18, there is shown an embodiment of an aircleaning apparatus according to the invention, which may form part of anHVAC system.

Electrostatic precipitation apparatus 60 is designed to remove unwantedaerosol particles from an air stream with high efficiency (typically99.99%) and comprises an air mover 65 in the form of a mechanical fan, aparticle charger 62, and a filter 66 for removing charged aerosolparticles from the air stream (“dirty air”) (not shown) as it flowsthrough the apparatus 60 in the volume defined by ductwork 69, in thedirection of arrow A, through the filter 66, to an outlet (not shown)downstream of the filter 66. Each of the particle charger 62, the fan 65and the filter 66 is provided within the ductwork 69, i.e. a housing toaccommodate said components.

The particle charger 62 comprises an electrode in the form of a singlepin 63 mounted centrally along the length of a rod 63 a that iselectrically coupled to a surrounding counter-electrode 63 b formed onthe interior surface of a portion of the ductwork 69 in the region ofthe pin 63 so as to enable corona discharge from the tip of the pin 63and the generation of air ions for charging aerosol particles in the airstream in the manner discussed earlier in this specification. The pin 63is illustrated in as an arrow which the arrowhead representing the tipof the pin. The counter-electrode 63 b is shown in dotted outline and isformed from conductive ink or paint applied directly to the interiorsurface of the ductwork 69. Alternatively, the ductwork 69 itself may bemade of a suitably conductive material. The rod 63 a on which the pin 63is mounted is fitted into the ductwork 69 by any conventional fixingmeans, including, for example, gluing, soldering, welding, etc.

As shown clearly in FIGS. 17 and 18, the particle charger 62 and the fan65 are provided upstream of the filter 66. Because the particle charger62 and the ductwork 69 together form the particle charging zone (havingair ion flow lines shown by the dotted arrows in FIG. 18) within whichaerosol particles will be electrically charged, and because the ductwork69 provides a hermetic seal between the particle charger 62 and the fan65 in the direction of air flow, all air entering the apparatus 60 viathe ductwork 69, has to pass through both the particle charger 62 andthe fan 65, such that charge bypass is eliminated.

Of course, the order of the components shown could be altered, in thatthe relative positions of the particle charger 62 and fan 65 could beexchanged so that the fan 65 is downstream of the particle charger 62(but still upstream of the filter 66). The position of thecounter-electrode 63 b would also need to be moved to match the positionof the particle charger 62, unless a greater proportion of the interiorsurface of the ductwork 69 were to be made conductive, or if theductwork 69 per se was conductive. The effect of elimination of chargebypass would nonetheless be the same.

It will be appreciated that certain features of the invention, which arefor clarity described separately, particularly those in the context ofalternative embodiments, may also be provided in combination in a singleembodiment.

Conversely, various features of the invention which are described incombination, in the context of a single embodiment, may also be providedseparately, or in any suitable combination.

It will also be appreciated that various modification, alterationsand/or additions to the described embodiments may be introduced withoutdeparting from the scope of the present invention, as defined in thefollowing claims. Many other possible modifications would be appreciatedby one of skill in the art following the teaching in this description.

1. An air cleaning device for removing aerosol particles from an airstream, the device comprising: (a) a particle charger comprising ahousing and an electrode arrangement therein for generating air ions inthe air stream, the particle charger having a particle charging zonewithin which, in use, aerosol particles in the air stream areelectrically charged via collision with the air ions; (b) a filter forprecipitating electrically charged aerosol particles from the air streammoving through the device; and (c) an air mover, comprising a casing,for moving the air stream through the device; wherein the particlecharger and the air mover are provided upstream of the filter; andwherein the housing of the particle charger is hermetically sealed tothe casing of the air mover in the direction of air flow through thedevice, such that the particle charger and the air mover are intimatelycoupled together, whereby all air entering the device has to passthrough both the particle charger and the air mover.
 2. (canceled)
 3. Anair cleaning apparatus for removing aerosol particles from an airstream, the apparatus comprising: (a) a housing comprising a first partof an electrode arrangement for generating air ions in the air stream;(b) a particle charger, located in the housing, and comprising a secondpart of the electrode arrangement for generating air ions in the airstream, wherein, together, the particle charger and the housing define aparticle charging zone within which, in use, aerosol particles in theair stream are electrically charged via collision with the air ions; (c)a filter, located in the housing, for precipitating electrically chargedaerosol particles from the air stream moving through the apparatus; and(d) an air mover, located in the housing, for moving the air streamthrough the apparatus; wherein the particle charger and the air moverare provided upstream of the filter; and wherein the housing provides ahermetic seal between the particle charger and the air mover in thedirection of air flow through the apparatus, such that the particlecharger and the air mover are intimately coupled together, whereby allair entering the apparatus has to pass through both the particle chargerand the air mover.
 4. The air cleaning device according to claim 1,wherein the particle charger and the air mover are intimately coupled asparticle charger/air mover in the direction of air flow.
 5. The aircleaning device according to claim 1, wherein the particle charger andthe air mover are intimately coupled as air mover/particle charger inthe direction of air flow.
 6. The air cleaning device according to claim1, wherein the filter is an electrostatic filter, an electrostaticprecipitator, a fibrous media filter, or an electret filter.
 7. The aircleaning device according to claim 1, wherein the air mover is amechanical fan, bellows, a convective airflow device or a centrifugalfan (a “blower”).
 8. The air cleaning device according to claim 1,wherein the electrode arrangement comprises two parts: an electrode anda counter-electrode.
 9. The air cleaning device according to claim 8,wherein the particle charger comprises both the electrode and thecounter-electrode.
 10. (canceled)
 11. The air cleaning apparatusaccording to claim 3, wherein the electrode arrangement comprises twoparts: an electrode and a counter-electrode, and wherein the first partof the electrode arrangement comprised in the housing is thecounter-electrode, and the second part of the electrode arrangement isthe electrode.
 12. The air cleaning device according to claim 8, whereinthe electrode is in the form of a pin or elongate wire, having a tip oran end.
 13. The air cleaning device according to claim 12, wherein theelectrode of the particle charger is supported on a support rod.
 14. Theair cleaning device according to claim 13 wherein two or more pin-typeelectrode are supported on a common conductor rod.
 15. The air cleaningdevice according to claim 8, wherein the counter-electrode surrounds theelectrode but is separated therefrom by a clearance.
 16. The aircleaning device according to claim 15, wherein the electrode issubstantially concentric with the counter-electrode.
 17. The aircleaning device according to claim 8, wherein the counter-electrode iscomprised of a plate having an aperture therein.
 18. The air cleaningdevice according to claim 8, wherein the counter-electrode comprises ahollow cylinder formed of conductive material or having a conductiveinterior surface.
 19. The air cleaning device according to claim 18,wherein the conductive interior surface is comprised of a conductive inkor paint.
 20. An air cleaning method for removing aerosol particles froman air stream and eliminating charge bypass, the method comprising:generating air ions in the air stream using a particle chargercomprising a housing and an electrode arrangement therein; electricallycharging aerosol particles in the air stream via their collision withair ions in a particle charging zone of the particle charger; and movingthe air stream towards a filter using an air mover comprising a casing,whereby electrically charged aerosol particles in the air stream areprecipitated onto the filter, wherein the housing of the particlecharger is hermetically sealed to the casing of the air mover in thedirection of air flow, such that the air stream is moved through anintimate couple of the particle charger and the air mover, whereby allair to be cleaned has to pass through both the particle charger and theair mover, prior to its arrival at the filter.
 21. (canceled)